I added a multi-lookup field to the standard event list on a modern experience communication site. Unfortunately the standard "New item form" does not show it. My idea is to display the classic newform.aspx in a model dialog inside a modern style webpart. I found out that SP.UI.ModalDialog is not available there and that office ui fabric should be used. I could not find any example which opens a web page inside a dialog, just static HTML. So here my questions:
What would be the best way to show the classic new, edit and view forms in a modal dialog on a modern sharepoint online page?
If it is possible to customize the modern new, edit and view event forms to allow attachments and multilookups that would be better actually, but I have no idea if its possible and how.
Thanks for any suggestions or hints for a maybe better approach.